1. Technical Field
The present invention is directed to high energy lithium ion batteries. More particularly, the present invention is directed to such a high energy density battery which incorporates carbon foam electrodes with each electrode having attached thereto an electrical contact plate.
2. Discussion
The dual graphite lithium battery was originally developed in the early 1980""s in an effort to provide a lightweight energy source capable of delivering very high energy density. The driving force behind the development of the lithium ion battery has been for some time the need for a lightweight and rechargeable power source embodying a high energy density for use in small electronic devices such as laptop computers and video cameras.
Additional applications of batteries demonstrating high energy density and light weight are being considered and explored. Specifically, electric vehicle applications are thought to be a promising use of this type of power source.
Electric vehicles, of course, are not new. Electric cars were introduced in the early 20th century which utilized aqueous-electrolyte type lead batteries. Lead batteries were satisfactory then (and remain satisfactory today) with respect to their good rechargeability. Because of the poor weight-to-energy-density ratio of the lead battery, these early electric vehicles proved slow and incapable of long distance operation.
Electric vehicles have traditionally been anachronistic, and, while offering the same modern appearance as their counterparts, have continued to suffer from the lead battery""s excessive weight and low energy density.
These problems have forced a shift in research to the lithium battery. Given the demand for a rechargeable secondary battery having an attractive energy density-to-weight ratio, much energy has been expended in studying various types of cells. Rechargeable lithium cells of many varieties have generated much interest. But the results have not been entirely promising. For example, rechargeable, nonaqueous electrolyte cells using lithium metal negative electrodes have presented several problems. Such batteries demonstrate poor fast charging properties and are notorious for their short cycle life. Great concern also exists for the inherent safety of the lithium battery largely the result of the irregular plating of lithium metal as the battery is cycled.
To overcome these problems while providing a power source that has application in electric vehicle technology, rechargeable batteries based on lithium intercalation are being researched. The lithium ion-based secondary cell is a nonaqueous secondary cell. Typically, lithium or a lithium salt is provided as an ion source which is intercalated into a carbon electrode to create a positively charged electrode.
Lithium ion batteries provide several advantages over known lead batteries, such as small self-discharge characteristics and, at least when compared to lead batteries, environmental safety. But the greatest advantage of lithium ion batteries over the known lead battery for vehicle application is attractive energy-density-to-weight ratio. Being lightweight while offering high energy density, the lithium ion battery is thought to have great potential in electric vehicle applications.
The cathode in a conventional lithium ion battery (typically a metal oxide such as Mn2O4, CoO2, or NiO) is doped with lithium. The conventional lithium ion battery uses a lithium salt (typically LiPF6 or LiClO4) dissolved in one or more organic solvents. When dissolved, the salt in the electrolyte is split into the positive ion and negative cation (depending on the salt used). The lithium ambient graphite fiber battery positive ion is intercalated into the carbon anode and the negative ion is intercalated into the carbon cathode.
When a charge is applied to the positive and negative electrodes, the lithium from the cathode is transported from the cathode as an ion and is intercalated into the anode (carbon or lithium metal). Voltage is created by the difference in potential of the positively charged anode and the negatively charged cathode.
On discharge, the process is reversed and lithium ions flow from the anode into the liquid electrolyte as do the negative ions from the cathode. The cell is balanced by equal parts of positive and negative ions absorbed back into the electrolyte.
Since the lithium ion moves from one electrode to the other to store energy the lithium ion battery is commonly known as a xe2x80x9crocking chair battery.xe2x80x9d The lithium ambient graphite fiber battery uses the same principal of intercalation for the positive electrode (carbon) and uses it again for the negative electrode (carbon). This is in lieu of a lithium doped metal oxide.
The lithium ambient graphite fiber battery is thought to be more attractive in electric vehicle applications. The lithium ambient graphite fiber battery, for example, is safer in principal than the lithium ion battery. In addition, while demonstrating a comparable theoretical energy density to the lithium ion battery, the lithium ambient graphite fiber battery will demonstrate more recharge cycles than a lithium ion battery.
A number of patents have issued which teach the general construction of the lithium ion battery. Such patents include, for example: U.S. Pat. No. 5,631,106, issued on May 20, 1997, to Dahn et al. for ELECTRODES FOR LITHIUM ION BATTERIES USING POLYSILAZANES CERAMIC WITH LITHIUM; U.S. Pat. No. 5,721,067, issued on Feb. 24, 1998 to Dasgupta et al. for RECHARGEABLE LITHIUM BATTERY HAVING IMPROVED REVERSIBLE CAPACITY; U.S. Pat. No. 5,705,292, issued on Jan. 6, 1998 to Fujiwara et al. for LITHIUM ION SECONDARY BATTERY; U.S. Pat. No. 5,677,083, issued on Oct. 14, 1997, to Tomiyama for NON-AQUEOUS LITHIUM ION SECONDARY BATTERY COMPRISING AT LEAST TWO LAYERS OF LITHIUM-CONTAINING TRANSITIONAL METAL OXIDE; U.S. Pat. No. 5,670,277, issued on Sep. 23, 1997, to Barker et al. for LITHIUM COPPER OXIDE CATHODE FOR LITHIUM CELLS AND BATTERIES; U.S. Pat. No. 5,612,155, issued on Mar. 18, 1997, to Asami et al. for LITHIUM ION SECONDARY BATTERY; U.S. Pat. No. 5,595,839, issued on Jan. 21, 1997, to Hossain for BIPOLAR LITHIUM-ION RECHARGEABLE BATTERY; U.S. Pat. No. 5,587,253, issued on Dec. 24, 1996, to Gozdz et al. for LOW RESISTANCE RECHARGEABLE LITHIUM-ION BATTERY; U.S. Pat. No. 5,571,634, issued on Nov. 5, 1996, to Gozdz et al. for HYBRID LITHIUM-ION BATTERY POLYMER MATRIX COMPOSITIONS; U.S. Pat. No. 5,567,548, issued on Oct. 22, 1996, to Margalit for LITHIUM ION BATTERY WITH LITHIUM VANADIUM PENTOXIDE POSITIVE ELECTRODE; U.S. Pat. No. 5,554,459, issued on Sep. 10, 1996, to Gozdz et al. for MATERIAL AND METHOD FOR LOW INTERNAL RESISTANCE LITHIUM ION BATTERY; U.S. Pat. No. 5,547,782, issued Aug. 20, 1996, to Dasgupta et al. for CURRENT COLLOZION FOR LITHIUM ION BATTERY; U.S. Pat. No. 5,496,663, issued on Mar. 5, 1996, to Margalit et al. for LITHIUM VANADIUM PENTOXIDE POSITIVE ELECTRODE; and U.S. Pat. No. 5,478,668, issued on Dec. 26, 1995, to Gozdz et al. for RECHARGEABLE LITHIUM BATTERY CONSTRUCTION.
Also among this group are several patents to McCullough, McCullough et al., or McCullough, Jr. et al. which include: U.S. Pat. No. 4,631,118, issued on Dec. 23, 1986, for LOW RESISTANCE COLLECTOR FRAME FOR ELECTRODONDUCTIVE ORGANIC, CARBON AND GRAPHITIC MATERIALS; U.S. Pat. No. 4,830,938, issued on May 16, 1989, for SECONDARY BATTERY; U.S. Pat. No. 5,503,929, issued Apr. 2, 1996, for LINEAR CARBONACEOUS FIBER WITH IMPROVED ELONGABILITY; U.S. Pat. No. 5,532,083, issued on Jul. 2, 1996, for FLEXIBLE CARBON FIBER ELECTRODE WITH LOW MODULUS AND HIGH ELECTRICAL CONDUCTIVITY, BATTGERY EMPLOYING THE CARBON FIBER ELECTRODE, AND METHOD OF MANUFACTURE; and U.S. Pat. No. 5,518,836, issued May 21, 1996, for FLEXIBLE CARBON FIBER, CARBON FIBER ELECTRODE AND SECONDARY ENERGY STORAGE DEVICES.
Particularly, the graphite component has taken on a variety of forms as evidenced by the prior art. For example, a supercapacitor based on carbon foams has been illustrated in U.S. Pat. No. 5,260,855, issued on Nov. 9, 1993, to Kaschmitter et al.x
While generally improving the state of the art, known battery designs incorporating carbon foam electrodes have not eliminated the need for a practical lithium battery construction.
It is an object of the present invention to provide a lithium ion battery incorporating carbon foam electrodes.
A further object of the invention is to provide a practical electrical contact on each of the carbon foam electrodes.
Another object of the invention is to provide an electrical contact having a channel formed therein for placement on and partially around an end of the carbon foam electrode.
Other objects and advantages will become apparent from the following detailed description and accompanying drawing. Basically, the invention comprises a battery having at least two carbon foam electrodes. Each of the electrodes is fitted with a plate formed from an electrically conductive material. The plate has an underside which is formed so as to be attached to one end of the carbon foam electrode. The plate may be fixed to the electrode by crimping or a similar deforming process.